Changes in body temperature and blood pressure in rats with calcium and magnesium deficiencies

Magnesium in hypertension: mechanisms and clinical implications

Hypertension is associated with increased risk of cardiovascular disease and death. Evidence suggests that Mg2+ depletion contributes to hypertension. It is estimated that 25% or more of the United States population experiences chronic, latent Mg2+ depletion. This review explores mechanisms by which Mg2+ influences blood pressure, modifying risk of hypertension and complicating its treatment. Mechanisms addressed include effects upon i) sympathetic tone, via the modulation of N-methyl-D-aspartate (NMDA) receptor and N-type Ca2+ channel activity, influencing catecholamine release from sympathetic nerve endings; ii) vascular tone, via alteration of L-type Ca2+ and endothelial nitric oxide synthase (eNOS) activity and prostacyclin release; iii) renal K+ handling, influencing systemic K+ balance and potentially indirectly influencing blood pressure; iv) aldosterone secretion from the adrenal cortex; and v) modulation of pro-hypertensive inflammatory processes in dendritic cells and macrophages, including activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome and stimulation of isolevuglandin (IsoLG) production. Discovery of these mechanisms has furthered our understanding of the pathogenesis of hypertension, with implications for treatment and has highlighted the role of Mg2+ balance in hypertension and cardiovascular disease.

The role of dietary magnesium deficiency in inflammatory hypertension

Nearly 30% of adults consume less than the estimated average daily requirement of magnesium (Mg2+), and commonly used medications, such as diuretics, promote Mg2+ deficiency. Higher serum Mg2+ levels, increased dietary Mg2+ in-take, and Mg2+ supplementation are each associated with lower blood pressure, suggesting that Mg2+-deficiency contributes to the pathogenesis of hypertension. Antigen-presenting cells, such as monocytes and dendritic cells, are well-known to be involved in the pathogenesis of hypertension. In these cells, processes implicated as necessary for increased blood pressure include activation of the NLRP3 inflammasome, IL-1β production, and oxidative modification of fatty acids such as arachidonic acid, forming isolevuglandins (IsoLGs). We hypothesized that increased blood pressure in response to dietary Mg2+-depletion leads to increased NLRP3, IL-1β, and IsoLG production in antigen presenting cells. We found that a Mg2+-depleted diet (0.01% Mg2+ diet) increased blood pressure in mice compared to mice fed a 0.08% Mg2+ diet. Mg2+-depleted mice did not exhibit an increase in total body fluid, as measured by quantitative magnetic resonance. Plasma IL-1β concentrations were increased (0.13 ± 0.02 pg/mL vs. 0.04 ± 0.02 pg/mL). Using flow cytometry, we observed increased NLRP3 and IL-1β expression in antigen-presenting cells from spleen, kidney, and aorta. We also observed increased IsoLG production in antigen-presenting cells from these organs. Primary culture of CD11c+ dendritic cells confirmed that low extracellular Mg2+ exerts a direct effect on these cells, stimulating IL-1β and IL-18 production. The present findings show that NLRP3 inflammasome activation and IsoLG-adduct formation are stimulated when dietary Mg2+ is depleted. Interventions and increased dietary Mg2+ consumption may prove beneficial in decreasing the prevalence of hypertension and cardiovascular disease.

Physiology of a Forgotten Electrolyte-Magnesium Disorders

Magnesium (Mg²⁺) is the second most common intracellular cation and the fourth most abundant element on earth. However, Mg²⁺ is a frequently overlooked electrolyte and often not measured in patients. While hypomagnesemia is common in 15% of the general population, hypermagnesemia is typically only found in preeclamptic women after Mg²⁺ therapy and in patients with ESRD. Mild to moderate hypomagnesemia has been associated with hypertension, metabolic syndrome, type 2 diabetes mellitus, CKD, and cancer. Nutritional Mg²⁺ intake and enteral Mg²⁺ absorption are important for Mg²⁺ homeostasis, but the kidneys are the key regulators of Mg²⁺ homeostasis by limiting urinary excretion to less than 4% while the gastrointestinal tract loses over 50% of the Mg²⁺ intake in the feces. Here, we review the physiological relevance of Mg²⁺, the current knowledge of Mg²⁺ absorption in the kidneys and the gut, the different causes of hypomagnesemia, and a diagnostic approach on how to assess Mg²⁺ status. We highlight the latest discoveries of monogenetic conditions causing hypomagnesemia, which have enhanced our understanding of tubular Mg²⁺ absorption. We will also discuss external and iatrogenic causes of hypomagnesemia and advances in the treatment of hypomagnesemia.

Time-course of the change in blood pressure level in magnesium-deficient Wistar rats

To investigate the relationships between maternal, umbilical cord and piglet fatty acid status, multiparous sows (six per diet) were fed on diets containing supplements (30 g/kg) of either soyabean oil or tuna oil for the last 21 d of pregnancy. The proportions of most fatty acids differed between diets: in particular, the tuna-oil-containing diet supplied more 22:6n-3 and less 18:2n-6 fatty acids than the soyabean-oil-containing diet. Maternal plasma fatty acid concentrations (mg/l) were greater than those in umbilical plasma and 20:4n-6 and 22:6n-3 fatty acids were present in higher proportions (g/100 g fatty acids) in umbilical than maternal plasma. Feeding tuna oil increased the proportionate amounts (g/100 g fatty acids) of total n-3 fatty acids (particularly 22:6n-3) in umbilical cord, plasma and piglet tissues compared with feeding soyabean oil: in contrast, the proportion of 20:4n-6 was decreased by feeding tuna oil. Changes in piglet fatty acid proportions as a result of oil feeding were not influenced by piglet weight. While proportions of the long-chain n-3 and n-6 polyunsaturated fatty acids in piglet liver, spleen and reproductive tract (ovaries plus uterus of the female, testes of the male) correlated well with those of umbilical plasma, those in brain and retina were poorly correlated. Therefore umbilical plasma cannot be used to predict the fatty acid status of piglet brain.

Enhancement of endotoxin-induced vascular hyporeactivity to phenylephrine in the thoracic aortas of Mg-deficient rats ex vivo

Since endotoxin lethality is enhanced by Mg deficiency in animals, we determined whether endotoxin-induced vascular hyporeactivity to phenylephrine (PE) is enhanced in Mg-deficient rats. Normal and Mg-deficient adult male Wistar rats were injected with Escherichia coli 011: B4 lipopolysaccharide (1 or 5 mg/kg, i.p.). Six h later, rings prepared from their thoracic aortas showed severe hyporeactivity to PE. This was more pronounced in the Mg-deficient rats, and was reversed by in vitro treatment with a highly selective inducible nitric oxide (NO) synthase inhibitor, 1400 W, or a highly selective soluble guanylyl cyclase inhibitor, ODQ. However, reversal required high doses of both inhibitors in Mg-deficient rats. Endotoxemia for 6 h was associated with elevated serum interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha levels, and strong TNF receptor mRNA expression in the abdominal aortas, which were significantly greater in the Mg-deficient rats. Treatment of the thoracic aortas, isolated from control and Mg-deficient rats before endotoxic challenge, with IL-1beta or TNF-alpha for 6 h in vitro caused hyporeactivity to PE, but its severity did not differ significantly between the two groups. These results suggest that high serum IL-1beta and TNF-alpha levels, and increased TNF receptor production in the vascular tissue, contribute to vascular hyporeactivity to PE in endotoxemia, and to its enhancement in Mg-deficient rats, via NO/cGMP signaling.

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

Influence of magnesium deficiency on concentration of calcium in soft tissue of uremic rats

The influence of magnesium (Mg) deficiency on the concentration of calcium (Ca) in the aorta, heart, and kidney was evaluated in uremic rats. A total of 32 rats were randomly assigned to two groups: one group made uremic by the 5/6 nephrectomy method, and the other serving as sham-operated controls. Both groups were randomly assigned to two subgroups: one group given a Mg-deficient diet and the other fed a Mg-supplemented diet. After 12 weeks on the regimen, all animals were sacrificed. In Mg-supplemented uremic rats, the concentration of Ca in the aorta was higher than in Mg-supplemented control rats. The concentration of Ca in the aorta was further increased in Mg-deficient uremic rats. The concentrations of Ca in the heart and the kidney were also increased in Mg-deficient uremic rats, as compared with Mg-supplemented uremic rats. The concentration of Mg was decreased in the aorta and increased in the kidney of Mg-deficient rats. There was no significant influence of Mg deficiency on the concentration of phosphate in tissue. Results suggest that Mg deficiency in uremia may increase aortic calcification.

Effect of low dietary calcium intake on blood pressure and pressure natriuresis response in rats: a possible role of the renin-angiotensin system

Dietary Ca is an important modulator of blood pressure in humans and rats. Since the kidney plays a key role in the pathogenesis of hypertension, the effects of a low Ca diet (0.01% Ca) on blood pressure and pressure natriuresis response were studied in normotensive Sprague-Dawley rats. In addition, a possible role of the renin-angiotensin system in the development of hypertension and an altered pressure natriuresis response resulting from low dietary Ca intake was examined. In the low Ca diet group, systolic blood pressure measured by the tail-cuff method was significantly higher than in the normal Ca diet group (1,1% Ca) 1 week after the diet (1 13.0 +/- 7.1 vs. 105.0 +/- 9.5mmHg, p < 0.05). After 4 weeks, the hypertension was more pronounced. Low dietary Ca intake significantly inhibited the water and sodium excretory responses to acute elevation of renal perfusion pressure by tightening an infrarenal aortic constriction. Treatment with an inhibitor of angiotensin-converting enzyme, captopril (30 mg/kg/day), completely abolished the elevation of blood pressure and attenuated the reduced pressure natriuresis response observed in Ca-deficient rats. Although plasma renin activity was not different between the low and normal Ca diet groups after the 2-week dietary regimen, the pressor response to angiotensin II was enhanced by 30% in the low Ca diet group and there was a significant difference in the pressor response between the two groups. These results suggest a possible involvement of the renin-angiotensin system in the development of hypertension and an inhibitory effect on the pressure natriuresis response caused by low dietary Ca intake, via an enhanced sensitivity to angiotensin II.

The effect of aging on the mineral status of female mice

To clarify the effect of aging on the mineral status of female mice, mineral concentrations in their tissues were determined. Five 2-mo-old, five 6-mo-old, and five 10-mo-old female B10BR mice were fed a commercial diet. Iron, zinc, copper, calcium, magnesium, sodium, and potassium concentrations in the blood, liver, kidney, heart, brain, lung, and spleen of the mice were determined using a flame atomic absorption spectrophotometer. Iron concentrations in the liver, kidney, heart, brain, and spleen increased with age. Significant differences were detected between mice 2 and 6 mo of age and between mice 2 and 10 mo of age. Zinc concentrations in the heart and lung decreased significantly with age. Zinc concentrations in the heart and lung of 10-mo-old mice were significantly lower than those of 2-mo-old mice. It is noteworthy that the copper concentration in the brain of 10-mo-old mice was markedly higher compared with that of younger mice. Calcium accumulation was apparent in the kidney of mice at 10 mo.

Elevation of blood pressure in young rats fed a low calcium diet. Effects of nifedipine and captopril

Hypertension was developed in 5-week-old male rats fed a low calcium diet, which evokes hypocalcemia and nutritional hyperparathyroidism, for 2 weeks. Blood pressure returned to normal after changing to a normal calcium diet. These changes of blood pressure were preceded by changes of calcium levels in plasma. In parathyroidectomized rats receiving a normal calcium diet, blood pressure did not rise, though the plasma calcium level decreased to a similar extent as in rats fed the low calcium diet. These findings seem to indicate that hyperparathyroidism, not hypocalcemia, is involved in the elevation of blood pressure in rats fed a low calcium diet. The elevated blood pressure was reduced by a calcium antagonist, nifedipine, but not by an inhibitor of angiotensin-converting enzyme, captopril. This may indicate that hypertension due to nutritional hyperparathyroidism responds to the calcium antagonist nifedipine and calcium supplementation, and is not dependent on renin.

Dietary magnesium does not affect blood pressure in spontaneously hypertensive rats

To determine the therapeutic effectiveness of dietary magnesium in the treatment of established hypertension, 21 male spontaneously hypertensive rats were fed altered levels of magnesium oxide from 17 to 29 weeks of age. The rats were divided into three groups of approximately equal mean baseline systolic blood pressures and fed AIN 76A purified diets containing magnesium at 0.01% (low), 0.05% (normal), and 0.40% (high) levels. Mean systolic blood pressures in the conscious SHR during the 12 week period and terminal direct blood pressures under anesthesia were not significantly different among treatment groups. Total and ultrafilterable serum magnesium concentrations reflected dietary magnesium intake. Total and ultrafilterable serum calcium levels were significantly higher (p less than 0.05) in the low magnesium-fed SHR. Histopathologic alterations indicative of aging did not differ among treatment groups. Therefore, in spite of altered serum mineral status, blood pressure and histopathology were not affected by dietary magnesium.

The effect of variable magnesium intake on potential factors influencing endurance capacity

Rats fed a magnesium (Mg) deficient diet have a lower endurance capacity than rats fed Mg adequate diets. The current study evaluates the effects of marginal, moderate, and severe Mg deficiencies on physiological and biochemical changes that may contribute to the reduced endurance capacity of Mg deficient rats. Variable levels of dietary Mg (400, 200, 100, 50 micrograms/g) were fed for 23 d to 5-wk-old male Osborne-Mendel rats. Indirect blood pressure and heart rate were measured during dietary treatment. Forty-eight hours after an endurance test, rats were killed and sampled for plasma glucose, insulin, and triglyceride levels. Organ weights, mineral and trace element concentrations, and carcass composition were determined. Blood pressure was lower in rats fed 50 and 100 ppm Mg during the first half of the study than in controls (400 ppm Mg). There were no significant differences in blood pressure among groups at the end of the study. Heart rate was not affected by dietary Mg intake. Plasma insulin was lowered by decreasing dietary Mg; however, plasma glucose and triglyceride concentrations were not affected by dietary Mg intake. Rats fed 100 and 50 ppm Mg diets had significantly higher calcium concentrations in plasma and gastrocnemius muscle than controls. Dietary Mg variably affected tissue trace element (iron, zinc, copper, and manganese) concentrations but did not affect Mg concentrations in any organ studied. Body composition was significantly altered by dietary Mg intake. In conclusion, variable Mg intake differentially affects the parameters evaluated. Thus, the decreased endurance capacity of the Mg deficient rat is apparently not the result of a single biochemical lesion but is likely to be multifactorial.

Effect of moderate magnesium deficiency on serum lipids, blood pressure and cardiovascular reactivity in normotensive rats

1. Weanling Wistar rats were pair fed for 10 weeks on a purified diet containing either normal or suboptimal quantities of magnesium (960 or 80 mg/kg respectively). 2. At week 2, hypomagnesaemia was accompanied by hypertriglyceridaemia, an increase in plasma cholesterol and a decrease in high-density-lipoprotein-cholesterol in animals fed on the Mg-deficient diet. At week 10, the increase in triglycerides observed in Mg-deficient animals was less marked while the increase in total cholesterol was more important. 3. During the whole experimental period, Mg-deficient animals never showed hypertension. At week 2, mean arterial blood pressure was significantly lower in Mg-deficient rats than in their respective controls, while heart rate was significantly increased. However, hypotension accompanied by tachycardia was a transitory phenomenon which appeared only in the early phase of deficiency. 4. Vascular reactivity was studied in vagotomized anaesthetized rats after ganglionic blockade with pentolinium and atropine sulphate. The reactivity to noradrenaline was significantly higher in Mg-deficient rats compared with pair-fed controls after 2 weeks on the experimental diet.

Effect of marginal calcium intake on blood pressure in the Wistar rat

Epidemiological studies in man suggest that blood pressures tend to be higher in persons with low calcium (Ca) intakes. Previous studies in normal rats have shown that severe Ca restriction raises blood pressure. The chronic effect of moderate Ca restriction is not known. We evaluated the effect upon systolic blood pressure of rearing young Wistar rats on a diet marginally adequate in Ca. Male weanling Wistar rats (8 rats per group) were placed on one of four diets containing 0.5% Ca (control diet), 0.4% Ca, 0.3% Ca, or 0.2% Ca. The three experimental diets were made up by replacing CaHPO4 in the salt mix with (NH4)H2PO4. Content of PO4 and electrolytes other than Ca was the same for all 4 diets. Sodium (Na) content was 0.1%. Diets were fed for 19 weeks. Rats did not grow normally on the 0.2% Ca diet, but growth was normal on the other three diets. There was no overall statistically significant effect of diet upon systolic pressure. During the first nine weeks of study there were no significant differences between groups and no consistent trends. During the last seven weeks, however, there was a consistent trend toward higher systolic pressures as Ca intake decreased. The mean change in blood pressure during the last five weeks of study from the baseline value at 4 weeks of age was significantly greater in rats consuming 0.2% Ca and tended to be greater in rats consuming 0.3 and 0.4% Ca than in controls. On several occasions, group mean systolic pressures were significantly greater in rats on the experimental diets than in controls. Systolic pressures for individual rats, averaged over the last seven blood pressure measurements, varied over a wider range in the experimental groups than in rats eating the control diet, and the distribution in the experimental groups was shifted toward higher systolic pressures. The results suggest that rearing normal rats on a diet marginally adequate in Ca may lead to a modest elevation in the blood pressures of some, but not all rats. The effect, however, is of much smaller magnitude than that observed with severe Ca restriction.

Influence of magnesium on blood pressure and the effect of nifedipine in rats

The influence of long-term alterations in dietary magnesium intake on blood pressure and on the antihypertensive effect of the calcium antagonist nifedipine was investigated in normotensive Wistar-Kyoto (WKY) and in spontaneously hypertensive rats (SHR). The rats were fed a diet either high (1%), normal (0.1%), or low (0.01%) in magnesium for 12 weeks (WKY) and 20 weeks (SHR), respectively. Nifedipine was added to the diet for 4 weeks in concentrations of 300 and 1000 ppm. Each dose was given for 2 weeks. Plasma and intraerythrocytic concentrations of sodium, potassium, and magnesium were measured before and at the end of nifedipine treatment. Blood was obtained by cardiac puncture. In the WKY and SHR, blood pressure was not influenced by magnesium intake. The blood pressure-lowering effect of nifedipine was most pronounced on normal dietary magnesium and was significantly suppressed in the magnesium-deficient rats. Plasma and intracellular total magnesium concentrations were consistently increased during high and reduced during low dietary intake of the ion. Intracellular sodium concentration increased during magnesium deficiency and was normalized by nifedipine. The marked and long-term alterations in plasma and intracellular concentrations of magnesium did not influence arterial blood pressure levels in either the normotensive WKY or the SHR. Therefore, dietary magnesium intake does not appear to play an important role in long-term regulation of blood pressure in rats. However, magnesium depletion attenuates the blood pressure-lowering effect of nifedipine.

Evidence against the role of calcium deficiency in genetic hypertension

Epidemiological studies suggest an association between reduced calcium uptake and hypertension, while clinical trials and rat experiments indicate a small but significant hypotensive effect with oral calcium supplements. These data imply that calcium deficiency has a role in genetic hypertension. We reasoned that if the hypothesis is correct, the hypertension should be aggravated by further reducing calcium balance but attenuated by augmenting calcium balance. We tested this hypothesis by evaluating the blood pressure response in spontaneously hypertensive rats (SHR) as calcium balance was decreased by dietary restriction of calcium or increased by supplementation with magnesium or 1 alpha, 25-dihydroxycholecalciferol (calcitriol). A low calcium diet within the physiological range did not accentuate the hypertension in SHR during the 11 weeks of treatment, even though calcium balance was reduced by half. Similar results were obtained with dietary calcium restriction in parathyroidectomized SHR, which excludes any offsetting effects of changes in parathyroid hormone levels. Conversely, 7 weeks of a high magnesium diet, which increased calcium balance without reducing PO4 balance, did not correct the hypertension of SHR. Similarly, long-term administration of calcitriol failed to reduce the blood pressure of parathyroidectomized SHR and normotensive Wistar-Kyoto (WKY) controls, despite the presence of increased serum calcium levels comparable to those produced by oral calcium loading. Finally, external calcium balance was measured directly in 25-day-old, prehypertensive SHR. As a result of the increased calcium absorption and reduced calcium excretion, SHR retained more calcium than did the normotensive WKY, which directly refutes the existence of calcium deficiency at this normotensive stage. These data do not support the role of calcium deficiency in genetic hypertension.

Low calcium diet enhances development of hypertension in the spontaneously hypertensive rat

Young (5 week old) spontaneously hypertensive rats (SHR) were fed diets modified with respect to their calcium content. Control rats were given a normal calcium diet (0.3 per cent). During the experiment the systolic blood pressure (SBP), heart rate and serum level of total and ionized calcium were measured. Three diets were studied :calcium-free diet (0 per cent, h1), low calcium diet (0.03 per cent, h2) and high calcium diet (1.2 per cent, H). The h1 diet induced a transitory increase (at week 2), then a long-lasting decrease in SBP for 12 weeks. Heart rate and calcemia were significantly decreased. The h2 diet enhanced the increase in SBP and lowered heart rate for 10 weeks. Level of total and ionized serum calcium were unchanged. The high calcium diet (1.2 per cent) attenuated the increase in SBP for 44 weeks and enhanced the heart rate for 16 weeks. The serum level of total calcium remained stable but that of ionized calcium increased significantly at week 7. These data clearly establish that, in young SHR, a low calcium diet enhances the development of genetic hypertension and confirm earlier works obtained with calcium enriched diets. Experimental and clinical data lead us to emphasize the importance of alimentary calcium in the hypertensive pathology.

Epidemiologic observations on the relationship between calcium intake and eclampsia

In Guatemala, the obstetric population has a very low incidence of eclampsia despite the presence of factors that would be expected to favor appearance of the disease. In this study, the eclampsia incidence and calcium intake for three countries, Guatemala (low eclampsia incidence, high calcium intake); Cali, Colombia (high eclampsia incidence, low calcium intake); and the USA (low eclampsia incidence, high calcium intake) have been compared. Crude rates for eclampsia incidence were adjusted to control the effects of well-documented predisposing factors: age, parity, and prenatal care. Results of the study support an association between calcium intake and development of eclampsia.

Preliminary evidence of the effect of calcium supplementation on blood pressure in normal pregnant women

In this study the hypothesis that calcium supplementation during pregnancy can modify blood pressure patterns in a population of normal pregnant women was tested. Thirty-six women with normal single pregnancies, between 20 and 35 years of age, in the second trimester of gestation (15 weeks), were randomly assigned to receive 1 gm of calcium per day (n = 11), 2 gm per day (n = 11), or a placebo (n = 14). No differences were observed at the times of admission into the study (baseline) in demographic and clinical variables or in the calcium intake of each group. Baseline blood pressure measures in several positions also were not different. After the initial blood pressure measures (fifteenth week), five follow-up blood pressure measures were obtained. The supplemented groups had significantly lower diastolic blood pressure than the control subjects between the twentieth and twenty-fourth weeks of gestation. Thereafter, an increase in the control group and the group receiving 1 gm of calcium was observed, but levels were similar at term. On the contrary, patients receiving 2 gm of calcium had blood pressure values that remained significantly lower throughout the third trimester. No differences or clear patterns were observed in the blood levels of calcium, magnesium, phosphorus, and proteins between and within groups during gestation. A possible explanation involving parathyroid hormone is attempted.

Radiation and brain calcium: a review and critique

Serious controversy pervades the scientific study of radio-frequency (RF) radiation and its biological effects. The issues range broadly from international differences in safe exposure standards to questions pertaining to the neurological symptoms purportedly induced by electromagnetic radiation. In a more specialized vein, there is great concern in the discipline about the influence of different sources of radiation on the activity of calcium in the brain. A principal and very realistic reason for this concern stems from the pivotal importance of calcium ions in the normal functioning of the brain in all of its myriad complexity. The purpose of the review is to critically evaluate from an unbiased and "non-involved" viewpoint the major findings on the possible interaction between calcium ions and various radiation sources. Background information is also considered as it relates even indirectly to hypothetical mechanisms that might be used to explain any possible shift in Ca++ ion kinetics. Finally, an inclusive critique is presented which deals with the bench-top methods and strategy used in the conduct of calcium-radiation experiments.

Rise of blood pressure in calcium-deprived pregnant rats

It has been postulated that calcium uptake is inversely related to blood pressure (BP) in animals and pregnant women. To test this hypothesis, 34 female, 142-day-old Wistar rats were studied prospectively. They were randomly assigned to either a calcium-free diet (16 rats) or a normal diet (18 rats). Weekly measurements of tail systolic BP showed a statistically significant increase in BP in the calcium-free group after 6 weeks of treatment. After 9 weeks on this diet, the animals were mated. Five in the control group and six in the calcium-free group became pregnant. Thereafter, both of these subgroups (pregnant and nonpregnant calcium-free diet) continued with significantly higher BP until they were put to death. Blood samples taken at the end of the study showed significantly lower values of calcium/magnesium (Ca/Mg) ratio, but higher inorganic phosphate in the group consuming a calcium-free diet. Blood pressure during the last 3 weeks of the study was significantly inversely correlated with the blood Ca/Mg ratio and directly correlated with magnesium and inorganic phosphate values. This article supports the hypothesis that a low-calcium diet is associated with high BP in pregnant and nonpregnant female rats.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.

Effect of subacute manganese feeding on serotonin metabolism in the rat

To clarify the effect of subacute manganese feeding on serotonin and mineral metabolism, Wistar rats were separated into two groups and fed two different diets, on a normal diet and another a manganese-supplemented diet. After 3 wk on these dietary regimens, the rats on the manganese-supplemented diet manifested the following abnormalities: blood pressure was decreased, brain serotonin was decreased, aromatic L-amino-acid decarboxylase activity in the brain was decreased, and manganese levels in heart, lung, and kidney were increased, whereas sodium, potassium, magnesium, and calcium levels in the brainstem were decreased.